Soluble carbon nanotubes were prepared by treating SWNTs with sec-butyllithium and subsequently using the generated carbanions as the initiator to graft PtBA and PtBA-b-PMMA onto the surfaces of SWNTs. The anionic polymerization initiated by SWNTs-bearing carbanions not only provides a powerful strategy for functionalizing SWNTs but also gives us knowledge of the sidewall chemistry of SWNTs. The results indicate that a carbanion born on SWNTs behaves like an anionic initiator with high steric hindrance.